The invention relates to a driving voltage adjusting device and in particular to method and device for adjusting driving voltage of a microelectromechanical optical (MEMO) device and a display using the same.
Current thin film technology has enabled the development of sophisticated integrated circuits. This semiconductor technology has also been leveraged to create microelectromechanical structures. Microelectromechanical structures, comprising microsensors, microgears, micromotors, and other microengineered devices, are typically capable of motion or applying force. Currently, microelectromechanical devices are being developed for a wide variety of applications as they provide the advantages of low cost and extremely small size (on the order of microns). For example, microelectromechanical optical (MEMO) devices are employed in display technology.
A microelectromechanical optical device, such as an interferometric modulator, comprises an actuator operated by vibration or movement. The actuator, however, may suffer from increased mechanical stress or deterioration of organic material properties when the microelectromechanical optical device is operated for a long time or under various ambient temperature conditions, lowering the performance of thereof and reducing reliability due to an unsuitable driving voltage.
FIG. 1 illustrates an interferometric modulator 100. As shown in FIG. 1, the interferometric modulator 100 comprises a transparent substrate 101 and an actuator 107 disposed thereon. The actuator 107 comprises a plurality of top electrodes 102, a bottom electrode 104, and a plurality of posts 106. Each top electrode 102 may be a stack layer disposed on the transparent substrate 101. For example, the top electrode 102 may comprise an indium tin oxide (ITO) layer and an overlying chromium layer. An insulating layer (not shown), such as a silicon oxide or aluminum oxide layer, is formed on each top electrode 102. The bottom electrode 104 acts as a mechanical layer for the actuator 107, comprising aluminum or nickel. The top and bottom electrodes 102 and 104 are separated by the posts 106 comprising, for example, photoresist materials, to form air gaps g therebetween.
Visible light may pass through the air gaps g from the transparent substrate 101 and be reflected from the bottom electrode 104, inducing interference. Visible light with various wavelengths may be formed by the interference and air gaps g to provide visible light with different colors. If a voltage (driving voltage) is applied between one of the top electrodes 102 and the bottom electrode 104, two electrodes 102 and 104 may make contact, as the right side of the interferometric modulator 100 shown in FIG. 1. When this occurs, light cannot pass through the air gap g, resulting in formation of a dark region. As mentioned, when the interferometric modulator 100 is operated under different ambient temperatures, the width of the air gap g may vary with the deteriorated organic material properties of the post 106. Here, the ambient temperature indicates that the environment temperature of the location where the interferometric modulator 100 is situated. That is, the ambient temperature may vary with different climates or locations. The varied width of the air gap g induces an unstable driving voltage between the top and bottom electrodes 102 and 104. Additionally, the unstable driving voltage may also be induced because the mechanical stress of the bottom electrode (mechanical layer) 104 is increased with increased operating time of the interferometric modulator 100.